A mortgage-backed security (MBS) is a type of asset-backed security that is secured by a mortgage or collection of mortgages. The mortgages are sold to a group of individuals (a government agency or investment bank) that securitizes, or packages, the loans together into a security that investors can buy. The mortgages of an MBS may be residential or commercial, depending on whether it is an Agency MBS or a Non-Agency MBS; in the United States they may be issued by structures set up by government-sponsored enterprises like Fannie Mae or Freddie Mac, or they can be "private-label", issued by structures set up by investment banks. The structure of the MBS may be known as "pass-through", where the interest and principal payments from the borrower or homebuyer pass through it to the MBS holder, or it may be more complex, made up of a pool of other MBSs. Other types of MBS include collateralized mortgage obligations (CMOs, often structured as real estate mortgage investment conduits) and collateralized debt obligations (CDOs).